A battery of tests of attentional behavior will be utilized to delineate aspects of attentional problems of hyperactive children and to provide objective evidence of the value of the central stimulant methylphenidate in the treatment of hyperactivity. Sixty-five children, ages 7 to 10 years, clinically designated as hyperactive will be included in this study. Initial testing will include administration of the WISC, PIAT, a battery of tests of attentional behavior, and completion of rating scales by parents and teachers. Methylphenidate will be initiated at a dosage of 0.2 mg/kg/day and increased at two week intervals as needed. All patients will be tested on the Children's Checking Task (CCT) given at two week intervals during drug stabilization. Behavioral ratings will be performed by parents and teachers at the same time as the CCT. The initial test battery will be repeated after 12 weeks for off-on drug comparisons. A placebo will be substituted for active drug for two weeks after the 12 week evaluation. The battery of attentional behavior tests will be administered and the rating scales will be completed at the end of the placebo period. Data will be analyzed to determine if performance on the attentional battery: (1.) can predict a favorable response to drug, (2.) can provide objective evidence of improved attentional behavior as a result of drug administration, and (3.) can be utilized to regulate dosage of methylphenidate. Additional goals of the project are to provide further data on a new test of sustained attention, the Children's Checking Test (CCT) and to substantiate utility of the attentional tests in measuring the response to medication.